


THE ?RE5ER^ 



or PIS 






^ 3A 



. 'i 




Qass. 
Book. 




337 




, >^ ' 







DEPARTMENT OF COMMERCE 

BUREAU OF FISHERIES 

HUGH M. SMITH, CommiMionw 



PRINCIPLES INVOLVED IN 
THE PRESERVATION OF FISH BY SALT 



By HARDEN F. TAYLOR 

Chief Technologist 
U. S. Bureau of Fisheries 



APPENDIX n TO THE REPORT OF THE U. S. COMMISSIONER 
OF FISHERIES FOR 1922 




Bur«au of Fisheries Document No. 919 



PRICE, 5 CENTS 

Sold by the Superintendent of Documents, government Printing Office 
Washington, D, C. 



WASHINGTON 
GOVERNMENT PRINTING OFFICE 
1922 



DEPARTMENT OF COMMERCE 

J. BUREAU OF FISHERIES 

HUGH M. SMITH, Commissioner 



PRINCIPLES INVOLVED IN 
THE PRESERVATION OF FISH BY SALT 



By HARDEN F. TAYLOR 

Chief Technologist 
U. S. Bureau of Fisheries 



Appendix II to the Report of the U. s. Commissioner 
OF Fisheries for 1922 




Bureau of Fisheries Document No. 919 



PRICE, 5 CENTS 

Sold by the Superintendent of Documents, Government Printing Office 
Washington, D. C. 

washington 
government printing office 

1922 






LIDF^ARY OF CONQFIESS 

FEB 2319^2 

DOOUMfcNTc Li.v.^ilON 



PRINCIPLES INVOLVED IN THE PRESERVATION OF FISH 

BY SALT. 



By Harden F. Taylor, 
Chief Technologist, U. 8. Bureau of Fisheries. 



Contribution from the Fisliery Products Laboratory, Washington, D. C. 



CONTENTS. 

Page. 

Introduction 1 

How salt preserves 2 

How salt extracts w^ater 3 

Factors affecting permeability of fish 5 

Flavors of salt fish 8 

Dry salting and brine salting compared 9 

Loss by fish of nutrients in brine 11 

Influence of method of cleaning fish on salting 13 

Improved method of salting fish especially for warm weather 15 

Scotch-cured herring 16 

Mild-cured salmon 16 

Behavior of fat during salting process 16 

Reddening of cod and haddock 18 

Recovery of brine 19 

Accessory chemical agents and other factors in salting 20 

Conclusions 21 

Summary 21 

INTRODUCTION. 

The art of preserving fish by means of salt is of great antiquity. 
It was practiced by the Phoenicians and Greeks and was brought to 
a high degree of perfection by the Romans. Mixed with spices, salt 
was used for the preservation of food on the shores of the Mediter- 
ranean and the outlying country in the time of Christ, reference being 
made in the Sermon on the Mount to a salt which has lost its savor, 
meaning a salt in which the spices have lost their aroma by evapora- 
tion. In the centuries following the art continued, both in the Occi- 
dent and the Orient, to play an important part in world economy, 
v^hakespeare put in the mouth of his most wonderful character, Fal- 
staff, the words : " If I be not ashamed of my soldiers, I am a soused 
gurnet"- — a pickled gurnard, the gurnard being held in such light 
esteem that it was a term of contempt. ^Whether " sousing " or pick- 
ling made the fish doubly contemptible had better be left to the phi- 
lologists to determine. Less than 25 years after Shakespeare wrote 
that play the Plymouth Colony landed in America and brought with 



' Appondix II to the Ueport of the TT. S. Commissioner of Fisheries for 1922. B. F. 
Doc. 019. 

» King Henry IV, pt. 1, Act IV, Scene II. 



2 U. S. BUREAU OF FISHERIES. 

them the arts of sousing and pickling fish. The descendants of the 
Pilgrims are still pickling fish around Cape Cod and particularly 
at Gloucester. 

To a great many people it may seem that science has contributed 
little or nothing to the improvement of methods of preserving fish 
by salt. Perhaps this view is shared by a considerable number of 
people who are engaged in the business of salting fish. To them it 
may appear that salting fish is just salting fish, and "that's all there 
is to it." It may be admitted readily that science has not so per- 
vaded and dominated the fish-pickling industry as it has other an- 
cient arts, but it has contributed something and is capable of con- 
tributing a great deal more, and here lies the purpose of this paper. 
That purpose is to present the rationale of salting and pickling fish, 
so that the reasons for the various steps and modifications will be 
readily understood and appreciated, to the end that the art ma}' be 
practiced more intelligently and successfully. It is a further pur- 
pose of this paper, by showing what the few attempts made by 
science have done for the art, to convince and persuade those on 
whom the industry depends for its existence and progress that science 
can be expected to do a great deal more than it ever has done if it 
is energetically studied and applied. 

HOW SALT PRESERVES. 

Salt preserves by extracting water. Spoiling is a series of chem- 
ical activities for which water is necessary; remove the water and 
spoiling is arrested. The removal of water by means of salt is in 
some senses a truer dehydration than actual drying in air, for changes 
of an undesirable sort take place in air drying that are never cor- 
rected, while salting may be done in such a way that few changes 
other than removal of water are brought about. The statement that 
salt preserves by extracting water is to be taken strictly and liter- 
ally, for salt has no peculiar preserving or antiseptic quality, as 
many people seem to think. Things live, die, and putrefy in the sea, 
which is one-tenth saturated Avith salt. But by sufficient concentra- 
tion salt, an otherwise almost inert, harmless substance, becomes a 
pov>'erful preservative, merely because, if concentrated sufficiently, 
it extracts water. 

The process of transferring water from one place to another, as 
from the inside of a fish to the outside, under the influence of con- 
centrated solutions, is known to physicists and chemists as osmosis. 
This principle of ospiosis is of almost universal application in 
nature and is used by men in the arts, but a good understanding of it 
is not common. By osmosis our food is taken from the intestines 
to the blood without any communicating opening. By osmosis 
oxygen is taken from the air into the blood without any leakage 
of blood. By the same principle the kidney tubules remove unde- 
sirable substances from the body while holding back all desirable 
substances. By osmosis the roots of plants select the necessary 
minerals from the soil. A weak sugar solution will readily ferment, 
but if made concentrated it destroys yeast and bacteria by osmosis 
and is therefore an excellent preservative of fruits. Salt is also a 
preservative by virtue of its concentration. Any other neutral min- 



PRESERVATION OF FISH BY SALT. 3 

eral substance equally soluble would preserve in the same way that 
salt does, but salt happens to be the only one that the human palate 
and stomach will tolerate. 

HOW SALT EXTRACTS WATER. 

At the risk of appearing verbose the writer undertakes to elucidate 
the principles that govern osmosis, because osmosis is nearly the 
whole principle of salting fish. Without a knowledge of osmosis 
people may salt fish successfully by rule, but without such a 
knoAvledge it is quite impossible to understand the process. 

If a thin animal skin or membrane separates two liquids and if 
the liquids are alike and of the same concentration, nothing happens. 
But if they are unlike and of different concentration, one or the 
other or both of the liquids will pass through the skin to the other 
side. This passage through the skin or membrane is called osmosis. 
Just what components pass through the membrane, in what direc- 
tion, and how much depend on many circumstances. For the pur- 
poses of salting fish water is always the liquid, plus wliatev<^r is 
dissolved in the water. The dividing membrane is the skin of the 
fish and the membranous inclosures of the microscopic cells of which 
the substance of the fish is composed. We thus have water and salt 
outside, cell membrane between, and fish juice, or protoplasm, in- 
side, and we desire to Iniow what will happen and how we can in- 
fluence the process to suit our needs. The quantity and direction 
of flow through the skin or cell membrane will depend on (1) the 
nature of the dividing membrane, and (2) the nature and quantity 
of the substances dissolved in the water on each side. 

The nature of the dividing membrane will be considered first. 
Almost any substance can be made into a thin film or membrane. 
Such things as glass, tin-foil, and mica may be exceedingly thin, 
but are totally impermeable and therefore uninteresting in the pres- 
ent connection. But other membranes or films, such as parchment 
paper, gelatin films, animal bladders, and goldbeater's skins are 
permeable to a greater or smaller degree. Suppose pure water were 
on one side of a membrane and water containing dissolved salt on 
the other. If the membrane is perfectly permeable to all constitu- 
ents, water will pass through to the salt solution and salt will pass 
through to the water, and these movements will continue until the 
two sides are alike and then stop. It is always the tendency for 
the two liquids to come to equilibrium, and they would do so if the 
membrane were perfectly permeable. Nearly all membranes, how- 
ever, permit a freer flow of the solvent, in this case water, than they 
do of the solute (that which is dissolved) . in this case salt. 

If the membrane permits the water to flow but absolutely prevents 
passage of a dissolved substance, the membrane is said to be semi- 
permeable. In the example taken above, of pure water on one side 
and salt solution on the other, if the rjiembrane were semipermeable 
then the water would pass through to the salt solution, but the salt 
could not get through to the water. The level of the pure water 
would fall and that of the salt would rise. The difference in liquid 
level would exert a pressure called osmotic pressure. Ideally semi- 
permeable membranes are not realized in nature, though some of the 



4 U. S. BUREAU OF FISHERIES. 

membranes in plants and animals approach ideal semipermeability 
while they are living. Ideal semipermeability with respect to par- 
ticular dissolved substances has been achieved and is found in living- 
organisms. 

It is to be remembered that in case of semipermeable membranes 
the solvent will flow from the less conicentrated to the more concen- 
trated side of the membrane, so that if we wish to extract water we 
need only to make the outside more concentrated than the inside. If 
we wish to add water, we make the outside less concentrated than the 
inside ; that is, we use pure water outside, as has sometimes been done 
unfairly to swell oysters and make them appear " fat." 

It is also to be remembered that the degree of permeability of mem- 
branes does not necessarily remain unalterable. The permeability 
of the membrane can very readily be changed, as will be seen later. 
There is reason for believing, for example, that the permeability of 
fish to salt increases after death — for stale fish strike through more 
quickly than fresh fish — and that permeability increases at tempera- 
tures near the freezing point of water. 

The tissues of fish consist mostly of cells. Each cell is a bag of 
semiliquid, like the white of egg. The surface of every cell either is 
or acts like a semipermeable membrane. If we surround the cell with 
water, the inside will be more concentrated than the outside and 
water will go in. If we surround the cell with strong salt solution, 
water will pass out to the salt. Some salt will also pass into the cell, 
which fact shows that the cell wall is not ideally semipermeable. 

But what of the protein wdthin the cell ? Why does it not come out 
while the salt is going in? In order to answer these questions it is 
necessary to pass from a consideration of the nature of the mem- 
brane in osmosis to a consideration of the nature of the dissolved 
substance. 

By a great many experiments it has been found that some dissolved 
substances never pass through membranes under any circumstances, 
while others will pass through some membranes. It is found that 
those which never pass through are also those which on drying out 
do not crystallize but shrink to a tough mass. They are called col- 
loids. Examples of them are glue, albumen, gelatin, and soap. The 
smallest possible particle of these substances is comparatively large, 
too large, we naay imagine, to go through the texture of the mem- 
brane. They are not only large of molecule but complex in structure. 
The bulk of animal bodies consists of colloids called proteins, dis- 
solved in water. The other class of substances, those that may pass 
through membranes and which on drying out crystallize in regular 
geometrical shapes, are the crystalloids. Examples of this class are 
salt, sugar, and like substances.. It is not to be supposed, however, 
that all crystalloids will pass with equal facility through any given 
membrane. Nearly all membranes are in some measure selective of 
particular crystalloids. The ideal semipermeable membrane permits 
none to pass, but as membranes degenerate from ideal semipermea- 
bility to complete permeability they permit more and more of these 
dissolved things to pass through. 

The phenomena of osmosis having been briefly reviewed, one may 
readily perceive the importance of applying the principles to the 
salting of fish. Salt is brought in contact with the exterior of the 



PRESERVATION OF FISH BY SALT. 5 

cell. It dissolves in some of the moisture, forming a saturated solu- 
tion. This solution is separated from the contents of the cell by a 
cell niembrane which is more or less semipermeable. Water passes 
out of the cell to the salt and the processes of decay are stopped be- 
cause of insufficiency of water. The membrane, not being absolutely 
semipermeable, permits some salt to enter and the fish remains salty. 
The contents left in the cell are proteins or the valuable food ele- 
ments of the fish which, being colloids, are not permitted by the cell 
membrane to pass out. Thus water is extracted, salt enters, and the 
fish is preserved. 

When the time comes to eat the fish the process is exactly reversed. 
The fish is bathed in pure water. The cell contents are more con- 
centrated than the exterior, so water passes in. The cell membrane 
is to some extent semipermeable, so the protein does not escape, but 
the salt does. This exchange is carried to a point where the meat is 
again plump and a sufficient quantity of salt has been removed. 

Thus by exposing the meat of fish to salt we have removed the 
water and caused some salt to enter the meat and have stored the 
fish. We have then by exposing the fish to water put water back 
in the cells and taken out the excess salt. The actual food material 
of the fish — the cell protein — is still where it was, for practical pur- 
poses unchanged. If every step has been scientifically correct we 
have at the end very nearly the fresh fish we had to start with. But 
there is the rub. At every turn it is possible to depart from the 
scientifically correct. The principles of osmosis here very briefly 
stated are the fundamentals of the art of salting fish. In all that 
follows there will be frequent occasion to refer to osmosis. 

FACTORS AFFECTING PERMEABILITY OF FISH. 

The preservation of fish by salt is practiced extensively in the 
cooler parts of the United States, but very little has been done south 
of Chesapeake Bay. The reason fish have not been salted in the 
warmer parts of the country is that the process has not been satis- 
factory. Repeated efi^orts to salt alewives on the St. Johns Eiver in 
Florida previous to 1920 uniformly resulted in failure. In 1918 re- 
search on this problem was undertaken under the immediate direction 
of the writer. The results of a part of this program were published.^ 

The hypotheses which guided this work were somewhat as follows : 
During the course of " striking through " the fish two things are 
happening — (1) the flesh is brealdng down by autolysis (a process 
to be explained later) and (2) the salt is penetrating the flesh. Salt 
arrests autohsis when it arrives, but considerable damage may be 
done before the salt has reached the innermost parts of the fish. Now, 
these two processes — salt penetration and autolysis — are running a 
race, so to say. If the salt penetrates to the innermost parts before 
autolysis has destro^^ed them, the salt wins the race and the fish is 
saved. If before the salt can get to tfie innermost parts they have 
been decomposed by autolysis to an intolerable degree, then autol3^sis 
wins and the fish spoils. High temperatures accelerate both proc- 
esses, but while accurate measurements have not been made we know 

' Trossler, D. K. : Some Considerations Concerning the Salting; of Fish. Appendix IV. 
Report of the IJ. S. Commissioner of Fisheries for 1{>19, 55 pp. B. F. Doc. No. 8S4. 
Washington, 1920. 



6 



U. S. BUREAU OF FISHERIES. 



by practical experience and by experiment that at a sufficiently ele- 
vated temperature the fish will invariably spoil if blood be present. 
Now, to make certain that the race mentioned shall always be won 
by the salt, we may do one of two things, namely, retard the rate of 
decomposition or accelerate the penetration of salt. Worldng at a 
lower temperature is the only practicable means of retarding de- 
composition, but since we desire a method suitable for warm climates 
it is necessary to accelerate penetration of salt. How can the salt be 
caused to penetrate fish more rapidly? 

The physiologists have shown that in living animals compounds of 
calcium, barium, and magnesium have a marked effect in retarding or 
arresting penetration of membranes. By examination of numerous 
analyses of commercial brands of salt it was found that the salts of 
calcium and magnesium are those nearly always present as impurities. 
A few of these analyses are given herewith : 

Analysis of Various Salts fob Cubing Fish.^ 



Substances present. 



Turks 

Island 

salt. 



Trapani , 
Italian 

salt. 



Iviza, 
Spanish 

salt. 



Diamond 

Flake, 

domestic 

salt. 



Leslie 
Velvet 

Grain, 
Califor- 
nia salt. 



Sodium chloride 

Calcium chloride 

Calcium sulphate 

Magnesium chloride . 
Magnesium sulphate . 
Sand, etc 



Per cent. 
96.52 



Per cent. 

95.82 

.32 



Per cent. 

98.05 

.49 



Per cent. 
99.78 



Per cent. 
99.96 



1.53 
1.20 



1.19 

1.75 
.15 



.37 
.00 
.00 
.00 



.067 
.00 
.010 
.022 



1 These figures represent analysis of single samples of each brand taken in the market and are not aver- 
ages of numerous samples. Not only is some variation in manufacture unavoidable, but the chemical 
djtermination of such small quantities of impurities is subject to small errors. Therefore it should not be 
expected that any purchased lot of salt would conform exactly to the composition shown here. The 
figures represent in a general way the degree of purity that can be expected. 

By appropriate methods of measuring the rate of penetration of 
salt into fish it was found that if absolutely pure salt is used a A^ery 
rapid penetration is obtained, but that even small additions (from 
I to 5 per cent) of these salts of calcium and magnesium cause 
a very pronounced retardation of penetration. For example, by 
appropriate methods of analysis it was found that pure salt pene- 
trated as deeply in less than five and one-half days as did salt con- 
taining 1 per cent calcium chloride in nearly seven days. Similarly, 
a salt containing 4.7 per cent magnesium chloride penetrated no far- 
ther in five days than pure salt did in three. In order to bring about 
a much more rapid penetration of the tissues then, we have but to 
obtain a salt free from these impurities. The time gained by the use 
of pure salt enables fish to be salted at a much higher temperature 
and yet not spoil. Fish were salted in an incubator room in Wash- 
ington at a temperature of 90° F. at first, rising to 100° F. — the 
hottest summer Aveather. No unpleasant odor developed, and the fish 
upon being cooked and eaten were pronounced excellent. 

There was a further and somewhat unexpected difference between 
the effects of pure and impure salts. The flesh of the fish salted by 
impure salt is white, opaque, or chalky in appearance and much 
harder or firmer in consistency ; that of fish salted Avith pure salt is 
translucent and somewhat yellowish and much softer. While the 
former Avhite. firm fish is the customary quality demanded in com- 



PRESERVATIOlSr OF FISH BY SALT. 7 

merce, there are strong reasons for believing the softer and yellowish 
fish produced in pure salt to be superior. There is reason for be- 
lieving that the whitening of the fish in impure salt is explained by 
the fact that the calcium coagulates the protein, just as heat by coagu- 
lating egg white causes it to be white and firm. But where there is 
no calcium in the salt the protein retains its natural translucency and 
yellowish color. The calcium in impure salt is retained by the fish, a 
matter that will be discussed later under the subdivision on flavor of 
salted fish. 

While no investigations appear to have been made on the influence 
of temperature on the permeability of fish flesh, investigations have 
been made on a great variety of other living things, so tliat it is prob- 
ably safe to generalize cautiously regarding such influences on fish. 
Osmotic pressure varies, approximately, as absolute temperature.* 
That is, if Ave double absolute temperature osmotic pressure is doubled, 
other factors being held constant. The range from 32 to 100° F, 
within which fish salting is usually done is, on the absolute scale, 
rather narrow (491.4 to 559.4° A.), so the maximum variation due 
to this cause would be about 14 per cent. It is, however, a com- 
mon experience in pickling fish that the warmer the temperature the 
more rapid the striking through, a difference too great to be accounted 
for by temperature variations of osmotic pressure. The cell mem- 
brane^ itself must change. Whether any more free permeability 
caused by warm temperature is permanent after the fish is chilled 
again is not known, but the question would be Avell worth investi- 
gating. Cold, when in the neighborhood of freezing, also promotes 
permeability, as has been proved by various experiments. It is quite 
possible that fish chilled to a point near freezing (as in the mild cur- 
ing of salmon) would strike through much more quickly than fish at 
the customary warmer temperatures. This matter also should be 
investigated. 

Stale fish — that is, fish whose cell membranes have " died " — are 
more permeable than fresh fish. Some fish Avere held in the labora- 
tory all day at a temperature of about 75° F. and toward night were 
salted in pure salt and put in an incubator at 100° F. By the next 
day they were struck through. The combination of stale fish, high 
temperature, and pure salt brought about extraordinarily rapid 
penetration. 

At this point mention should be made of another effect of salt 
upon the protein constituents of fish. Strong solutions of salt pre- 
cipitate certain protein substances, different substances falling out 
successively from a mixture of dissolved proteins as the concentra- 
tion of salt is increased. The nature of the proteins is not altered 
by this precipitation, for upon replacement of the salt solution with 
fresh water the proteins redissolve and appear to V^e restored to 
their original condition. Salt thus causes a temporary precipita- 
tion or fixation of proteins in fish, to ascertain extent hardening the 
tissues and reducing the likelihood of changing. Not only does 
quite pure salt penetrate the fish more rapidly, but when the time 
comes to cook the fish it is found to soak out more rapidly also. 
Practical experiments in the experimental kitchen of the Bureau of 



* Absolute temperature is based on absolute zero, the point of no beat, or absolute 
cold which i.s —273° C. or —4");). 4° F. If we use degrees the same size as Fahrenheit 3 
degrees, then (»° F. is 4ii9.4 absolute; ,50° F. Is 4o9. 4 + 50=500.4 ab,soIute, etc. 

77635°— 22 2 



8 U. S. BUREAU OF FISHERIES. 

Fisheries indicate that fish preserved in very pure salt soak out in 
from a third to a half the time required by fish preserved in crude 
salt. 

What is the practical lesson of this work? It shows that by the 
judicious selection of salt, not on the basis of its cheapness but on the 
basis of composition, one can produce a salt fish of almost any 
desired quality'. If salting is to be done in very warm weather it 
will be necessary to use the purest grade of salt to secure very rapid 
penetration. In this way a soft, yellowish fish of excellent quality 
is obtained. Where weather is cool enough to permit, a salt contain- 
ing more calcium and magnesium may be used, in which case a 
whiter and firmer fish will be produced. 

Can these very pure salts be obtained commercially? Several 
brands of salt of the highest degree of purity are available both on 
the east and west coasts and at a cost not much above the price of 
cruder salt. In many cases the single item of fish saved that might 
otherwise spoil will repay the extra cost of pure salt, to say noth- 
ing of the improvement in quality of the salt fish. 

FLAVORS OF SALT FISH. 

The calcium and magnesium are taken up by the protein in the 
cells and held, not coming out when the fish is soaked. Now, these 
impurities, particularly calcium, have an acrid taste and greatly 
accentuate the " saltiness " of salt. Pure salt is not so " salty " to the 
taste as crude salt. If the calcium is held by the tissues at the time 
of soaking out while the salt is removed, then after soaking there is 
a much greater amount of calcium present in proportion to the 
amount of sodium than there was in the original salt and a corre- 
spondingly more acrid " salty " taste. It is therefore necessary to 
soak out fish much longer or until they are " flat " if they have been 
cured with crude salt, while with pure salt they may be soaked out 
until they suit the taste, after which they retain their original flavor. 

Certain improvements in the flavor of fish have been noted after 
they have been salted by improved methods. The fish variously 
known as mud shad or gizzard shad {Doroso77ia cepedianum) is 
plentiful in certain parts of the country but is held in very low esteem 
because of its muddy, unpleasant flavor. After being washed free 
from blood and salted in pure salt this unpleasant flavor disap- 
peared and the fish compared favorably with fish commonly more 
esteemed. The muddy taste of the carp and other fish from muddy 
ponds and streams is believed by some to be caused by species of 
Oscillatoria, a blue-green alga growing in the slime of the fish; by 
others it is believed to be humic acid derived from the mud. Per- 
haps the two views could be entirely reconciled, but the actual 
chemical compound or compounds responsible for the unpleasant 
flavor seems to be removed by the brine. 

It is not difficult to understand how the alteration of taste may 
be brought about by salting. The main bulk of the fish, pure protein 
and pure fat, is believed to be tasteless and odorless. The substances 
which give rise to taste are free fatty acids (decomposition products 
from fats), amino acids (decomposition products of proteins), highly 
odoriferous tiiethylamines, and various waste materials classed by 
the chemist as purines. The absolute quantities and also the relative 
proportions of these materials vary froni^ species to species of fish, 



PRESERVATION OF FISH BY SALT. 9 

and they even change in the same individual fish as staleness de- 
velops. Now, most of these odoriferous substances are soluble in 
water or brine, and after the salting process woukl be found in the 
brine. They are not replaced when the fish is soaked out. It might 
therefore be anticipated, as has actually been found, that the fresh 
fish, disagreeable because of the presence of strong substances, are 
rendered sweet by the removal thereof in the salting process. 

If this lead were followed in detail, it is quite possible that salting 
would turn out to be the best method of utilizing fishes that are of 
a rather poor edible quality when in the fresh condition. This aspect 
of the matter deserves particular attention of the canners. Many 
species of fish of great abundance might in time be profitably packed 
if the flavor were inviting. With highly improved technique in 
salting, the undesirable flavors might be removed by curing and 
soaking out before canning. This process would be unthinkable on 
the basis of the customary salting methods where there is in the 
end an excessive saltiness or flatness of flavor, but the mild, sweet 
fish prepared by improved technique and pure salt is a much more 
promising possibility for canning. 

DRY SALTING AND BRINE SALTING COMPARED. 

The next question taken up in the investigations referred to was 
that of the relative merits of the application of the salt to fish in 
the dry state and as a concentrated brine. In the Chesapeake Bay 
region the herring are usualh'^ pickled in brine. By a strict compari- 
son of the two methods it was found that there is developed a smaller 
quantity of the products of decomposition — the amino acids — when 
the salt is applied dry. Not only this, but it was also found that salt 
applied in the dry condition penetrates the fish more rapidly. 

Among the products of protein decomposition are amino acids. 
A determination of amino acid nitrogen was taken as a measure of 
decomposition — the more of the amino acid nitrogen present the 
greater the amount of decomposition. This being true, the following 
table, summarized from Tressler's results, will show the superiority 
of dry salt over strong brine for preserving fish. 

Amounts of Amino Acid Xitrocjex Formed Per Kilogram of Fish at Diffesent 

Temperatures. 



Method of salting. 



Tem- 
pera- 
ture. 



Amount of amino acid nitrogen per 
kilogram offish after — 



19 

hours. 



67 
hours. 



5 days. 



7 days. 



9 days. 



Condition 

at end of 

salting 

period. 



Dry salted. . 
Brine salted 
Dry salted.. 
Brine salted 
Dry salted. . 
Brine salted 
Dry salted.. 
Brine salted 
Dry salted. . 
Brine salted 
Dry salted.. 
Brine salted 



' F. 
63 
63 
70 
70 
75.5 
75.5 
80 
80 
87 
87 
93 
93 



Grams. 

0.078 

.08i( 

.084 

.077 
.102 
.074 
.086 
.076 
.097 
.065 
.080 



Gra ins. 
0. 083 
.129 
.086 
.165 
.092 
.186 
.086 
.189 
.089 
.244 
.105 
.238 



Grams. 
0.085 
.135 
.098 
.158 
. 099 
.179 
.119 
.210 
.159 
.266 
.151 
.320 



Grami. 
0. 085 
.183 
.097 
.190 
.104 
.228 
.141 
.300 
.195 
.377 
.193 
.465 



Gram^. 
0.119 
.234 
.126 
.292 
.134 
.316 
.158 
.383 
.208 
.510 
.236 



Good. 

Do. 

Do. 

Do. 
Fair. 

Do. 

Do. 
Spoiled. 

Do. 

Do. 

Do. 

Do. 



10 



U. S. BUREAU OF FISHERIES. 



It is seen that the brine-salted fisli consistently uncler<;o a greater 
decomposition than those salted with dry salt, as shown by the 
abundance of decomposition products, amino acids. The average 
excess of amino acid nitrogen in the six lots pickled in brine over 
the six lots in dry salt is 51 per cent, a very material difference. It 
Avill be noticed in the last column of the table that spoiling of fish 
]jickled in brine takes place at a lower temperature than it does in 
dry salt. Fish were satisfactorily salted in dry salt at 80° F., but 
at this temperature fish pickled in brine spoiled. 

To complete the evidence in favor of using dry salt, the following 
table from the, same paper shows the rate of ])enetration of salt into 
squeteague when applied dry in comparison with brine: 

Penetration of Salt. 





Section of fish. 


Percentage chlorine in dry sample after— 




1 day. 


4 days. 


7 days. 


10 days. 


Dry salted 


Outer layer, from surface to a 
depth of J centimeter. 

Inner layer, from J to 1 centi- 
meter below surface. 

Outer layer, as above 


9.8 

2.6 

8.4 
1.8 


16.2 

11.0 

15.3 
8.3 


19.6 

16.0 

17.3 
12.2 


19.5 


Do 


18.7 




17.8 


Do 


Inner laver. as above.. . 


15.7 







What is the reason for the superiority of dry salt over strong 
brine or pickle, especially since the dry salt very shortly forms its 
own pickle ? In answer to this question it is necessary to refer to the 
principles of osmosis. It was shown that the flow of water is from 
the less concentrated to the more concentrated. The relative con- 
centrations govern the direction of flow and also the rate or quantity 
of flow. Salt is going into the fish and water coming out. If brine 
is used, it is losing some of its salt which penetrates the fish and is 
being diluted with water which is coming out. This process rapidly 
brings the contents of the cells into equilibrium with the brine ; that 
is, with the film of brine immediately in contact with the fish. Stir- 
ring as usually done may cause a momentary increase of penetration 
by removing the film of dilute brine adjacent to the fish, but we may 
imagine that a new dilute, film forms again very rapidly. If instead 
of brine dry salt is placed in contact with the fish very material dif- 
ferences are at once apparent. Part of the salt dissolving in the 
free moisture forms strong brine, which begins its extraction of water 
from the fish. The water coming from the fish is not able to dilute 
the adjacent brine, because some of the excess of dr}^ salt present 
iromediately dissolves, and thus assures saturated brine at all times. 
It should also be obvious that since the very purpose of using salt 
on fish is to extract water the addition of water at the beginning 
simply supplies just so much water to the salt and satisfies the 
affinity of salt for water to that extent. The water should come from 
the fish and not elsewhere. 

To put into words the conclusions from this section of the paper, 
when salt is applied dry to the fish there is a more rapid penetration 
of salt, less decomposition of fish, and it is possible to preserve fish 



PRESERVATION OF FISH BY SALT. 11 

at a higher temperature. The superiority of dry salt over brine 
resides in the fact that the brine in contact with the fish is not per- 
mitted to be dihited if salt is present in crystalline condition. 

LOSS BY FISH OF NUTRIENTS IN BRINE. 

The liquid that comes from fish during the salting process is not 
pure water, as every fisherman knows, but contains a quantity of 
material derived from the fish. Most of the nitrogenous matter 
found in brine represents just so much good food gone to waste and 
just so many pounds of fish that might have fetched a good price 
gone overboard. The quantity of protein that escapes into the brine 
is highly variable, for reasons that will appear later. That some 
idea may be had of the magnitude of the loss of fish substance in 
brine the following figures are given. These figures were obtained 
in the course of investigation on the recovery of valuable materials 
from old brine : 

fx)ss BY Fish of Nutrient Materials in Brine. 





Brine. 


Grams 

dry 
protein 
per liter 
of brine. 


Avoirdu- 
pois 
ounces 

per 
gallon. 


Rockfish brine from Alaska 


29.30 
34.80 
73.30 


3.9 


Herring brine from Gloucester 


9.8 


Cod brine from Gloucester 


4.6 







Since all the nitrogen in the brine was calculated as protein, these 
figures are undoubtedly too high ; but the bulk of the nitrogen is cer- 
tainly of protein origin, so the figures may be taken to illustrate the 
point made. If we assume fresh fish to be 75 per cent water and 25 
per cent dry protein and express the results in customary units, the 
figures show the equivalent amount of food-fish flash dissolved in 
brine to be 15.6, 39.2, and 18.4 ounces, respectively, or from 1 to 2| 
pounds to the gallon of brine. Bitting ^ calculated the losses in the 
curing of codfish as follows : Loss of weight in dressing, 40 per cent ; 
loss in salting, 40 per cent of what remained after dressing ; drying 
on flakes, 9 per cent of the salted fish. The 40 per cent of the dressed 
fish contains besides water much protein or valuable nitrogenous food. 
It would certainly seem to be worth our while to examine into the 
causes of this loss and to prevent or salvage it if possible. 

How does this protein get out of the fish? It was said above that 
protein is a colloid and that colloids do not diffuse through mem- 
branes. A small amount must come from the blood and from the cut 
surface on the fish, but most of it will probably be found to'come from 
the interior cells by a process not yet investigated. We do know 
something directly about autolj^sis, however, the great enemy of the 
fish dealer, which liquefies the contente of fish flesh, and we have 
every reason to believe that if autolysis were stopped the losses of 
protein into brine would be reduced to a minimum. What is autolysis 
and how does it do its damage? 

^Bitting, A. W. : Preparation of Cod and Otlier Salt Fish for Market. IT. S. Depart- 
ment of Agriculture, Bureau of Chemistry, Bulletin No. 133, 63 p. Washington, 1911. 



12 U. S. BUREAU OF FISHERIES. 

Protein, the colloid, can not pass through an osmotic membrane, 
but proteins can be decomposed into simpler substances which readily 
dissolve and pass through. The agency which breaks down protein 
into these simpler substances is called an enzyme, and protein must 
always be so liquefied or digested by enzymes before it can be ab- 
sorbed through membranes; hence the necessity of digestion in the 
stomach of animals preparatory to absorption of food through the 
intestines. Now, animals, including fish, require a certain amount of 
new protein to support the body activities, Avhich, failing, the animal 
would immediately perish. But the hazards in the existence of any 
animal often make it obligatory to do without food for a shorter or 
longer period. If the stomach became empty because of temporary 
shortage of food or an injured mouth, the animal would die unless 
special provision were made to supply protein from some other source. 
But nature has provided a means whereby the proteins in the less im- 
portant parts of the body can be used for the time being to support 
the activities of the absolutely necessary vital parts. The stored pro- 
tein is within cells and could not possibly be carried by the blood 
stream to the point of need unless it could get out. So there is in 
each cell stored along with the protein some enzyme ready in case of 
threatened starvation to break the protein down into simpler sub- 
stances which penetrate outward into the blood for transportation to 
the point of need. Fish may thus live for a time at the expense of 
their own bodies. 

These enzymes, present in every part of the fish, while almost an 
absolute necessity to the living fish, become the greatest enemy of 
the dead fish, for they soften and liquefy the cell contents, cause 
unpleasant tastes and odors, and permit the contents to escape from, 
the cell into brine. The proteins could not escape as long as they 
were proteins, but when they are broken down by autolysis into sim- 
pler substances the latter rapidly diffuse into the brine and are lost. 
This at least is the hypothesis, supported by some facts. 

What factors promote autolysis and what factors oppose it? 
Warm temperatures promote it directly. A temperature sufficiently 
high to destroy the enzyme stops it. Low temperatures retard it 
directly. 

If cells are ruptured, as they often are hj rough handling of the 
fish, autolysis rapidly decomposes the protein, and for this reason 
every bruise received by the fish during capture and subsequent han- 
dling results in the loss of so much protein during salting. A bruise 
on a fish has about the same effect as does a bruise on an apple, pro- 
moting rapid decomposition. Perhaps if the bruised fish turned 
brown, as the bruised apple does, the fisherman and packer would 
be more easeful in the handling of their fish. 

Factors that increase permeability of membranes seem to promote 
autolysis. Low temperatures seem to increase the permeability of 
the cells, so that fish that have been chilled decompose more rapidly 
on being warmed than fish that have never been chilled, though as 
long as the fish remain on ice the low temperature may prevent the 
enzymes from doing their work. It is as if increased permeability 
increases the escape of the enzymes, and that once escaped they play 
havoc if temperature conditions are allowed to become favorable. 
The optimum temperature for autolytic activity is about humaii body 



1 



PRESEKYATIOiSr OF FISH BY SALT. 13 

temperature. 98° F. The autolytic enzymes act under a slightly acid 
condition. In neutral or alkaline medium they act very little, if at 
all. It has been noticed by A^arious investigators that autolysis does 
not begin until two to four hours after death. During rigor mortis 
there is a decided development of acid that may very materially pro- 
mote autolysis. It may therefore be that salting fish immediately 
after capture would strike through the fish before autolysis gains 
any headway. It may be possible, also, to take advantage of the 
removal of soluble products by brine in the salvaging of fish on the 
point of spoiling. Fish that have been held a long time are soft 
and of a disagi^eeable odor, because autolysis and possibly some bac- 
teria have decomposed the tissues to some extent. 

One might reasonably expect research to show that if rapid pene- 
tration is secured by means of pure salt the amino acids and other 
sour or disagreeable substances in stale fish resulting from autolysis 
would be removed by changing brine a few times, leaving the fish 
in a condition quite wholesome and fit for food. It is, of course, not 
intended here to encourage the practice of holding fish until they are 
bad and then salting them, but it is recognized that it is in the 
public interest neither to destroy food that can be used nor to mar- 
ket fish unfit for food, and it is recognized as legitimate and desirable 
to develop a means of saving fish whenever they have, through the 
unavoidable exigencies of the fishing business, come near to spoiling. 

It w^ould not be profitable to present this complicated subject any 
further here. Enough has been said to show that the loss in salting 
fish by solution of protein in brine is very great. Some discussion 
has been j^resented which will serve to show that losses of this kind 
are preventable, to point out the probable direction in which the 
remedy for this great loss will be found, and also, we hope, to assist 
in convincing the skeptics that scientific work on this aspect of the 
salting process would be worth while. It is of the greatest impor- 
tance that research work be undertaken for the purpose of discover- 
ing the conditions under which the cell proteins are digested and 
pass out and for ascertaining the conditions under which these proc- 
esses may be arrested. Specifically, such questions as follow should 
be answered: Once the permeability of cells has been increased 
by abnormally high or low temperature, does this increased per- 
meability persist after a normal temperature has been restored? 
When autolysis is set in action bj^ a bruise, do autohi:ic enzymes 
affect only the part bruised or do they escape and attack the unin- 
jured cells, destroying them also? To what extent does the acid of 
rigor mortis accelerate autolysis, and can this acceleration be pre- 
vented by early application of salt? To what extent is loss of solu- 
ble material in brine due to rough handling and to what extent to 
other factors? Can advantage safely be taken of the removal of 
products of protein decomposition by brine to salvage fish that are 
on the point of spoiling? „ 

INFLUENCE OF METHOD OF CLEANING FISH ON SALTING. 

In the various processes of salting or pickling fish the fish receive 
no preliminary treatment, or they may be gibbed, beheaded, split 
through belly, split through back, or cleaned perfectly by being cut 



11 



U. S. BUREAU OF FISHERIES. 



open, scraped, and washed before the salt is applied. By what cri- 
teria can we judg:e the merits of these various methods? The best 
way to answer this question is: Other conditions being held con- 
stant, which method or methods of cleaning result in least decom- 
position during the salting process? 

A series of trials was made by cleaning the fish by the various 
methods and salting them by the same process and determining the 
amounts of amino acid nitrogen developed. Two sets complete were 
tried, one consisting of one sample each cleaned by the various 
methods and held at a temperature of 79° F. during the salting 
process; another set similar to the preceding but held at 88° F. 
during the salting process. Both temperatures are high for salting 
fish, and the test is correspondingly severe. The results are shown 
in the following table, which is abbreviated from the paper by 
Tressler : 

Development of Amitvo Acid Nitrogen in Fish Cleaned in Various Ways. 

[Fish salted four hours after capture, with Diamond Flake salt containing 99.78 percent sodium chloride;' 

salting period, nine days.] 



Method of cleaning. 





Amino 




acid 




nitrogen 


Average 


formed 


tempera- 


during 


ture of 


salting 


salting. 


period 




per kilo 




of fresh 




fish. 


. op_ 


Grams. 


79 


0.77 


79 


.63 


79 


.68 


79 


.37 


88 


1.12 


88 


.76 


88 


.82 


88 


.47 



Condition of fish at 
end of period. 



No cleaning, salted round 

Pipped : 

Head cut off, abdominal cavity split open, viscera, except 
nult and roe, removed. 

Cleaned perfectly, nult and roe removed, kidney and mem- 
branes scraped, and all blood washed out. 

No cleaning, salted roimd 

Pipped 

Head cut off, abdominal cavity split open, viscera, except 
milt and roe, removed. 

Cleaned perfectly, milt and roe removed, kidney and mem- 
branes scraped, and aU blood washed out. 



Badly spoiled, bloated. 
Spoiled. 
Do. 

Excellent condition. 

Badly spoiled, bloated. 
Badly spoiled. 

Excellent condition. 



Since amino acid nitrogen indicates decomposition, the conclu- 
sions from this table are entirely obvious. Only those fish were 
successfully salted at temperatures of 79 and 88° F. which had been 
thoroughly cleaned and from which all blood had been removed. 
While these high temperatures were chosen for the test because severe 
tests bring out diiferences in a more striking way, the differences will 
still exist even at low^er temperatures and manifest themselves in the 
poorer or better quality of product. Now, it may be either the blood 
or flesh, or both, in which the decomposition takes place. Since the 
perfectly clean fish decompose only slightly, it may be that only the 
blood decomposed in such cases as those given in the table, and that 
the decomposed blood pervading the otherwise sound tissue gave the 
appearance and odor of decomposition to the whole fish. On the 
other hand, it is possible that the enzymes in the blood when present 
operate to decompose not only the blood proteins but the tissue pro- 
teins also. However, this may be, the indisputable fact remains 
that if fish are to be salted in very warm weather it is absolutely 



PRESERVATIOiSr OF FISH BY SALT. 15 

obli<j:atoiy that the blood be removed. The blood can not be re- 
moved by mere evisceratincy and rinsing in water. The kidney, a 
very bloody orp;an inclosed by a membrane against the backbone, 
must be scraped out before the fish is washed. If fish is cleaned in 
this manner and salt of a very pure quality applied in the dry con- 
dition, it is astonishing not only Avhat severe temperatures it will 
stand, but also how excellent it is when cooked. 

IMPROVED METHOD OF SALTING FISH ESPECIALLY FOR WARM 

WEATHER. 

Several factors have now been shown to have a marked influence 
on the quality of fish pickled in salt, namely, care in handling before 
salting to prevent bruises, use of salt free from calcium and mag- 
nesium (less than 1 per cent total impurity), packing in dry salt, 
and thorough cleaning and removal of kidney and blood. By com- 
bining all these factors into one method highly satisfactory results 
under the most adverse conditions have been obtained. 

A trial of the method was made in the herring season of 1920 
(March, April, and May) on the St. Johns Eiver, Fla. This region 
Avas selected because it offered a combination of the conditions sought. 
The climate is excessively warm, and there is an abundance of fish 
(alewives) adapted to preservation by pickling in a region where an 
industry might well be built up and where repeated efforts to salt 
fish in the past had failed. Accordingly, the interest of local fisher- 
men and dealers was enlisted to cooperate in the undertaking, and an 
experienced fish packer from the Chesapeake Bay region was sent 
to Florida, after he had been thoroughly instructed in the technology 
of the process, to try salting by the proposed method on a small 
commercial scale. 

The details as conveyed to the fishermen for handling the fish were : 
(1) Avoid (a) bruising the fish in removal from gill nets, (h) walk- 
ing on, and (c) piling deep in boats; (2) salt as soon as possible; 
(3) wash and scale in cold water; (4) behead and eviscerate and (a) 
scrape out kidney or (6) split nearly through to the back and lay 
open; (5) wash in weak brine to remove all traces of blood; (6) rub 
with fine salt of a high degree of purity and pack backs down in a 
barrel, leaving fish lightly covered to form their own brine; (7) after 
they have been struck through pack down and add other fish of the 
same lot to fill barrel; and (8), in conclusion, (a) head up barrel and 
pour saturated brine into bunghole to cover fish for storage, or (h), 
if to be sold for consumption at once, take out of the brine and rub 
in fine dry salt, then pack in sugar barrels or other light containers 
and ship immediately. 

The results fully justified expectations in every way. The fish 
were preserved successfully, and none that had been handled in the 
prescribed way spoiled. In eating qualities the}'^ were pronounced 
as good as or better than the best comnlercial salt herring from the 
('hesapeake Bay region. In order to test the absolute necessity of 
the prescribed methods, other small batches were put up in different 
ways — by using cheaper salt, leaving roes in, and other such modifica- 
tions. I'hese trials were failures without exception. About 80,000 
fish were packed by the prescribed method and marketed the first 
rear. 



16 U. S. BUREAU OF FISHERIES. 

The successes and failures under these extremely adverse conditions 
tell us much about what could be expected under more favorable con- 
ditions. What succeeds under severe conditions will be a finer prod- 
uct under more favorable conditions, and what spoils under severe 
conditions will be an inferior product under conditions in which it 
does not actually spoil. It should be noted that the product prepared 
by this method is mild and sweet, approaching very closely fresh fish 
in eating qualities, if it has been properly soaked out. 

SCOTCH-CURED HERRING. 

The discussion in this paper so far presupposes the desirability of 
preserving as far as possible the flavor and eating qualities of fresh 
fish. The Scotch cure does not involve this supposition but aims 
directly at giving the cured fish a new and distinct flavor from partly 
decomix)sed or fermented blood, the purpose being the same as that 
governing the flavoring of cheese by ripening. The blood is not 
removed, the fish rather being allowed to cure in its own blood pickle, 
a distinctive flavor thereby being imparted. They are gibbed, rubbed 
with dry, fine salt and packed, more fish being added to make up for 
shrinkage, and shipped or stored in the original blood pickle. This 
method is suitable for cold but not for warm climates. Since, how- 
ever, Scotch-cured herring come in a special class of fermented 
products where different motives and processes are concerned, the 
method will not be further discussed here. 

MILD-CURED SALMON. 

In the preservation of salmon by salting advantage is taken of the 
naturally cool temperatures prevailing in the Northwest, so that the 
extreme of dehydration by salt is not necessary. Even here no 
chances are taken, for in most instances the casks of mild-cured 
salmon are held in cold storage at about 38° F. The selection of salt 
is principally on the basis of fineness, because a fine-ground salt is 
necessary to stick to the moist fish, only that which sticks to the fish 
being used dry. It appears that in the mild curing of salmon some 
of the principles already referred to may be important. It was 
pointed out that calcium and magnesium salts combine with the fish 
protein to form a white, hard flesh. In the case of salmon it is desir- 
able to preserve the red color which is contained in the fat, but the 
precipitation or coagulation of the otherwise transparent protein is 
in all probability the cause of whitening, which masks the attractive 
red color of the fat. Also, what was said about the loss of nitroge- 
nous matter as a consequence of bruises applies to the mild curing of 
salmon. 

BEHAVIOR OF FAT DURING SALTING PROCESS. 

So far in this paper discussion has been limited to the behavior 
of the protein or meat constituents of fish. It will be found that fat 
is also of the greatest importance and requires very careful considera- 
tion and study. All fishes have some fat, but the quantity is variable 
from species to species, between individuals of the same species, and 
within a single individual from season to season. The distribution 
of fat is also diiferent in different species of fish. Some fishes, such 



PRESEEVATIOISr OF FISH BY SALT. 17 

as herring, salmon, and alewives, contain fat well distributed through- 
out the body tissues. In others, such as cod and haddock, the fat 
is localized in some particular part of the body, as in the species 
mentioned the oil is contained in the lever, the flesh being almost 
entirely destitute of oil. For reasons that will be set forth later fat 
fish must not be exposed to the air because of untoward changes that 
air causes in the fat ; but no harm is done to the protein constituents. 
Therefore fish which do not contain fat may be dried in air after 
they are salted. 

In practice these differences are well recognized. In the case of 
cod and haddock, in which the muscle tissue is free from fat, the 
greater part of free water is extracted in the usual way by salt, 
later assisted by the pressure of piles or kenches, in which the lower 
layers are pressed by the weight of the upper layers in the kench, 
and finally by drying out of doors or in artificial drying tunnels. 
Fish prepared by this method are packed and shipped in the dry 
state, with advantages in saving of freight and simpler handling in 
general. In the case of mackerel and herring and such other fishes 
as have fat tissues the fish must at all times be carefully excluded 
from contact with air. If the fish are directly exposed to air for a 
time, the fish " rust " — that is, the fat becomes reddened and rancid — 
and the value of the fish for food is very greatly impaired. This 
rusting, especially of salt mackerel, is of immediate and pressing 
practical importance, for there is a regular waste of a large per- 
centage of mackerel on our northeastern coast for no other cause than 
rustiness and rancidity. This aspect of the subject has not been in- 
vestigated to any great extent, but there is just as much reason to ex- 
pect valuable results to accrue from work on this problem as have 
accrued from the work already described. 

Fats consist of a combination of glycerin with fatty acids. In 
the absolutely pure state, which is scarcely attainable, in fact, they 
would presumably be colorless, odorless, and tasteless. They usu- 
ally contain a greater or smaller quantity of coloring matter dis- 
solved, and under certain conditions the combination, glycerin-fatty 
acid, may be broken down, free glycerin and free fatty acid resulting. 
Free fatty acid has both taste and odor ; in fact, our choicest fishes, 
such as salmon, shad, and mackerel, owe much of their peculiarly pala- 
table flavor to the small amount of free fatty acid present. But 
many of the free fatty acids of fish oils readily oxidize on exposure 
to air and light, developing during the process a darker color and 
an unpleasant odor and taste which we call rancidity. Once fats 
have become rancid they can never be restored to their original 
sweetness. 

Wliat conditions promote rancidity? First, the fat must be de- 
composed or " split " into glycerin and free fatty acid. Next it must 
oxidize. Just as fish contain autolytic enzymes that decompose pro- 
tein, so they also contain fat-splitting enzymes. These enzymes re- 
quire moisture and warmth for their activities. Fat that has been 
removed from the tissue that produced it may be kept under proper 
condition for a long time, because only a small amount of fat-split- 
ting enz5'me goes with the oil, but when the fat is not removed from 
the original source all the enzyme is present and available to produce 



18 U. S. BUREAU OF FISHERIES. 

decomposition. So in salt fish the fat is in tlie presence of moisture 
and an abundance of enzyme, and the necessary warmth is usually 
present also, ideal conditions for decomposition. The fat having 
been split to fatty acid, there are two factors, so far as known — 
namely, air and light — which promote oxidation. 

Some little stud}' has been devoted to the effect of salts, such 
as sodium chloride and calcium chloride, on the splitting of fats, 
but not enough is known about the effect of these substances in con- 
centration to be of any assistance. Whether or not bruises have the 
effect in promoting decomposition of fat that they have in promot- 
ing decomposition of protein is not known but would be well worth 
knowing, and here further investigation is certain to be of value. It 
is known that much of the fat in living fish is contained w^ithin in- 
closed cells, and that even the fattest fish is not greasy when fresh. 
But whenever the cells are ruptured by rough handling, decomposi- 
tion or whatever cause, the oil escapes and is exposed to all the un- 
favorable influences of enzymes, moisture, air, and light, and the 
fish becomes greasy ; eventually it will become rancid. And, further, 
oil escaped from the fish, being of a lower specific gravity than 
brine, at once rises to the top of the barrel and is lost as food. 

All sorts of possible preventives of rust are practiced or suggested 
for practice — such things as impermeable barrels, air-proof covering 
over the liquid, a reducing substance in the brine to absorb 
the oxygen, cool, dark storage, and the like. There is, of course, 
much dissolved oxygen in the juice of the fish and in the brine and 
also considerable amounts of free oxygen occluded in the cavities 
of the fish to effect considerable rancidity, even if all outside air is 
excluded. This dissolved and occluded air can be removed by a 
vacuum pump, but this has never been tried commercially, so far as 
the writer is aware. Very little improvement can be expected until 
the problem has been thoroughly investigated by scientific methods. 
In the improved technique recommended by the Bureau of Fisheries 
in Florida complete covering of the salt fish by brine in tight barrels 
was specified. 

REDDENING OF COD AND HADDOCK. 

If cod and haddock escape rusting because of lack of fat, they 
are subject to another enemy perhaps as bad, namely, reddening, by 
which large quantities of cod and haddock are lost every year. For 
the past three years work has been conducted by the division of 
scientific inquiry of the Bureau of Fisheries on the causes of redden- 
ing and significant results have been obtained. The cause, in gen- 
eral, has been known for many years to be bacteria, but otherwise 
little has been known of the origin of these bacteria or of their 
peculiarities. 

Briefly stated, the results of the work cited are as follows: The 
bacteria that cause reddening are of two distinct kinds — a spirochaete, 
which in colonies is pale pink, and a bacillus whose colonies are deep 
red. The two organisms grow in such close harmony that mixed 
colonies occur which vary in color from pale pink to deep crimson 
as the proportions of the two organisms present vary. The evidence 
points to the solor sea salts from the tropical and subtropical seas 
as the source of the infection. Solar sea salts, both American and 
foreign, are infected. Mined salts seem to be free from the infection. 



PRESERVATION OY FISH BY SALT. 19 

Every species of bacteria is acclimated to some particular set of 
conditions, some of them almost incredible for living things. These 
red bacteria are accustomed to live and grow either on moist salt or 
ver^^ strong salt solutions. If bacteria are particularly resistant to 
some condition, as to strong salt in this case, it does not follow that 
they are likewise resistant to all severe conditions. It is the bac- 
teriologist's business, by studying all the habits and peculiarities of 
the organism, to discover its weakest point where attack will destroy 
it. The strongest resistance of these bacteria, that against salt, is 
also the weakest, for it has been found that water less than 15 per 
cent saturated destroys them. Thus, the present indications are that 
the best and simplest remedy for the trouble is clean, fresh water 
and plenty of it. There is some evidence that may support the view 
that the usual impurities in salt, calcium and magnesimn compounds, 
are essential to the growth and multiplication of these bacteria. 
The implication here is, of course, that pure salt itself would be a 
poor supporter of the bacteria. Of course, it would be futile to try 
to stop the reddening of cod as long as every shipment of salt brings 
new infection, and the butts, floors, buildings, and the surroundings 
at packing plants are heavily infected. Facts already given indi- 
cate also that for other reasons salt free from impurity is better. 
The results of the study of reddened cod only emphasize this advice. 

The research on reddening should not, however, end here. We are 
again dealing with questions of permeability. The bacteria are ad- 
justed to strong salt solutions, that is, the body fluid is of such con- 
centration and their coA'ering membrane is of such partial perme- 
ability that when surrounded by strong salt solution they live nor- 
mally, but when water or weak brine surrounds them these relations 
are disturbed and they die. Probably water enters the cell in ex- 
cessive quantity. It is known that the reddening does not attack 
fat fish. Perhaps the fat acts directly on the membrane, or indi- 
rectly by acting on the calcium and magnesium in the salt, to effect 
the disturbance. 

RECOVERY OF BRINE. 

Even crude salt now costs considerably more than coal. Yet the 
fish packers, who are usually very careful to economize in coal, are 
prodigal in the use of salt. Every hundred pounds of brine that 
goes overboard contain about 26 pounds of salt, to sa}' nothing of the 
A'aluable nitrogenous matter that the brine has extracted from the 
fish. Considerable work has been done by the writer and his as- 
sociates on the development of a process to recover salt and other 
substances of value from old pickle by precipitating the proteinace- 
ous matter with sodium silicate. A trial plant was in use and under 
observation at an important fish-packing establishment for over a 
year but was not satisfactory under the circumstances. Brine pure 
enough for use was recovered, while a substance very rich in 
nitrogen was yielded as a by-product. This substance in the dry 
condition is nearly white and friable and contains enough nitrogen 
to command a handsome price as fertilizer if suitable for that pur- 
pose, but it may be more valuable for other uses. The method re- 
covered brine, and for this reason some other method that would pro- 



20 U. S. BUREAU OF FISHERIES. 

(luce dry salt may be better. The experience gained in the Avork 
already done indicates that the recovery of vahiable material from 
brine would not go well as a part of a small fish business but, having 
its own peculiar problems, would be more properly conducted as a 
separate business. In any event, this promising subject is com- 
mended to the chemists and engineers for study. We can not doubt 
that a few years will bring forth a complete solution of the prob- 
lem of recovering things of value from brine that will make us 
wonder why we ever threw it away. 

ACCESSORY CHEMICAL AGENTS AND OTHER FACTORS IN SALTING. 

Various other chemicals are sometimes used in salt or along with 
it for various purposes. Some of these will be briefly discussed. 

Saltpeter performs two functions in brine for the preservation of 
meat, namely, it combines with the red substance of blood, hemo- 
globin, which is unstable, to form a j^ermanently stable red deriva- 
tive, nitroso-hemoglobin. By virtue of its oxidizing power it may 
also oxidize hj^drogen sulphide into sulphur dioxide and water ; that 
is, a very foully odoriferous stuff to a substance which both bleaches 
and sterilizes. Saltpeter is, however, little used in curing fish, for 
the red color is undesirable, and hydrogen sulphide is rarely trouble- 
some. 

Boric or boracic acid is sometimes added to the final application of 
salt to dried salt cod. This is to prevent reddening. Undoubtedly it 
does do so, and undoubtedly most of it is removed from the fish when 
the latter is soaked up before cooking. Nevertheless, it seems that 
the end of this practice is not distant. Boric acid has long ago been 
condemned as a food preservative. With the comparatively small 
amount of scientific investigation that has already been done we have 
reason to hope that not only can reddening be prevented, but that 
by the general refinement and improvement of methods it will be- 
come unnecessary to use artificial preservatives to prevent reddening. 

A method of promoting the preservation of fish by salt by the aid 
of sodium hypochlorite along with the salt has been patented. The 
original idea, it is understood, was to decompose the salt in sea water 
by electrolysis, sodium hypochlorite being formed. It was claimed 
that the sodium hypochlorite penetrates faster than ordinary salt. 
This substance contains some oxygen that may be given off to act as 
a sterilizing agent, and after the oxygen is given off ordinary salt 
or sodium chloride remains. What advantages the process possessed 
are not altogether apparent, for nothing appears to have come of it. 
It may be said, however, that sodium hypochlorite readily destroys 
urea, so that this substance might be advantageous in the preservation 
of grayfish and sharks but is unstable and must be used as soon as 
it is made. 

The size and shape of the fish obviously have much to do with the 
time required for salt to penetrate through. Salt effects no preserva- 
tion of parts until it reaches them. A thick fish may spoil, while a 
thin fish may be saved; hence the splitting of fish. Other methods 
of applying the salt to the inner parts of fish may be used, such as a 
needle syringe, whereby the brine is forced into the tissues, and com- 
pressed air, which is used to force brine into fish after the excess air 
has been removed from them in vacuo. It should also be possible 



PRESERVATION OF FISH BY SALT. 21 

to insert a needle in the gill arch and with pressure completely irri- 
gate the whole system of arteries and veins of a fish, removing abso- 
lutely all the blood at one stroke without cutting the fish. 

CONCLUSIONS. 

The preservation of fish by means of salt is an excellent method, 
even in the crude and inexact manner in which the art has hitherto 
been practiced. The comparatively small amount of scientific re- 
search that has been done on the problems and principles involved 
has not only justified itself in practice but furnishes abundant 
grounds for the expectation that a great deal more of valuable results 
will follow further work. It is not mere guesging to say that when 
advantage is taken of all that is known of improved salting methods 
a fish nearly if not quite equal in edible qualities to fresh fish is ob- 
tained, and in some cases the quality is decidedly improved by salting. 

There is every reason to expect a good future for the salt fish in- 
dustry, but progress must be made. Preservation by this method is 
eminently practicable, simple, and reliable for holding and transport- 
ing our sea fishes to the inland population. 

SUMMARY. 

1. A discussion of the principles involved in the preservation of 
fish by salt has been presented. 

2. Salt possesses no inherently peculiar preserving qualities, but 
preserves food by extracting water. 

3. The principle by which salt (and other soluble substances) in 
concentrated solution extracts water is called osmosis. Osmosis is 
the passage or interchange of liquids and solutions through mem- 
branes which are more or less permeable. The permeability of cell 
membranes in fishes appears to be affected by high and low tem- 
peratures. The presence in or absence from the salt of certain im- 
purities, notably calcium and magnesium compounds, the treatment 
of the fish, and the staleness of the fish, are factors which govern the 
permeability and have an important bearing on the preservation of 
fish by salt. 

4. Calcium and magnesium compounds in addition to retarding 
penetration cause a whitening and hardening of the fish. There are 
chemical reasons for looking upon this whitening and hardening by 
these compounds as undesirable. 

5. The flavor of fish is often altered by the salting process. Cal- 
cium salts retained in the tissue increase the salty taste and make 
necessary a prolonged soaking out. Undesirable flavors of fishes 
from muddy waters may sometimes be removed by salting the fish. 

6. Salt applied dry penetrates the fish more rapidly and effects a 
quicker cure with less danger of spoilage in warm weather. 

7. There is a very material loss oP protein material from fish 
during the salting process. This material probably arises from the 
decomposition products ordinarily unable to pass out of the cells but 
which are digested by autolysis, an internal destructive process. 

8. Autolysis is increased by crushing, bruising, rough handling, 
pewing, elevated temperatures, low temperatures followed by a rise, 
and, in general by factors that increase cell permeability. It is 



22 IT. S. BUREAU OF FISHERIES. 

retarded or arrested by continued low temperatures, sufficiently high 
temperatures, and by salt. 

9. The damage done by autolysis appears to be in large part pre- 
ventable. 

10. Fish containing blood, or otherwise not well cleaned, spoil at 
a lower temperature than those thoroughly cleaned and freed from 
blood. Thoroughly cleaned fish may be salted at from 90 to 100° F. 
if pure salt is used. 

11. A method of curing fish embodying the improvements cited 
was tried in Florida on a small commercial scale with gratifying 
success. 

12. Scotch-cured herring develop a peculiar flavor which is derived 
from the fermentech or otherwise altered blood. This method has 
for its aim an alteration to suit particular tastes, while other meth- 
ods of salting discussed aim at the preservation of the fresh qualities 
of fish. 

13. There are reasons for expecting that the improvements made 
in the salting of other fish, particularly those which depend on the 
use of a very pure salt, will find application in the mild curing of 
salm.on. 

14. Fats undergo certain changes after the fish is salted, resulting 
in a condition known as " rusting." Rusting consists of oxidation 
of fat after the latter has been split into free fatty acids. This split- 
ting is caused by tissue enzymes in the presence of warmth and mois- 
ture. Oxidation is brought about through the agency of light in 
the presence of water. While rusting causes large losses of fish, the 
means of preventing it, such as tight barrels, air-tight covering, and 
cool dark storage, are not very satisfactory. The problem demands 
further investigation. 

15. Fishes whose flesh is not fat and therefore not prone to rust 
are subject to damage by reddening. Reddening is caused by two 
organisms, a spirochaete and a bacillus. They may be destroyed by 
fresh water or live steam. They originate probably in solar sea salt 
and are apparently not found in mined salt or other purified Ameri- 
can salt. 

16. Some work has been done toward the development of a process 
for recovery of salt and other valuable materials from brine. There 
are a number of promising possibilities which should make this an 
attractive field for chemists and engineers. 

17. Certain substances are sometimes used as adjuncts in salting 
fish. Saltpeter preserves a pink color and neutralizes hydrogen sul- 
Ijhide. Boric acid is used for preserving cod against reddening. 
Sodium hypochlorite has been proposed as advantageous in conjunc- 
tion with salt. It may be produced electrol3i;ically from sea water. 

18. The size and shape of the fish influences the rate of penetration 
of salt into it. Certain mechanical methods of forcing brine into 
large fish may be advantageous. 

o 



LIBRARY OF 



CONGRESS 



002 877062 5 




